The invention relates to a sealed arrangement consisting of a housing and a cylindrical insert.
Crankcases for engines and compressors are frequently composed of light, soft materials, such as, for example, aluminum. These materials are unsuitable for the cylinder running faces along which the pistons slide. Cylinder liners composed of harder materials and along which the pistons slide during operation of the engine or compressor are therefore inserted into corresponding cylinder bores in the crankcase. The cylinder liners have to be sealed here in relation to the crankcase. This applies in particular whenever the cylinder liner encloses a cooling duct with the crankcase.
Cylinder liners are generally inserted into the crankcase either in a loose fit or in an interference fit. In the case of a loose fit, the cylinder liner can move within the crankcase during the subsequent operation, which impairs the tightness. In the case of an interference fit, the seal (O-ring) attached between cylinder liner and crankcase can be mechanically damaged, and this can no longer be checked after the cylinder liner is fitted into the crankcase.
It is therefore the object of the invention to provide an arrangement consisting of a housing and a cylindrical insert having improved sealing.
This object is achieved according to the invention by an arrangement according to the embodiments of the invention. Further advantageous refinements emerge are described and claimed herein.
Within the scope of the invention, an arrangement has been developed consisting of a housing with a receptacle or opening and a cylindrical insert which is fitted into the receptacle or opening with at least one interference fit. Cylindrical is understood as meaning not only circular cylinders. The cylinder may also have an elliptical or polygonal area.
According to the invention, the insert has an encircling groove, and therefore said insert is both fastened and sealed in a liquid and/or gas-tight manner against the housing by the material of the insert and/or the housing, which material has been pushed into the groove during the installation.
The cross section of the groove can have any desired shape. The simplest to manufacture are grooves with a rounded cross section, for example with a radius of curvature of between 0.5 and 1.5 mm. However, V grooves or other grooves with a polygonal cross section, such as, for example, rectangular grooves, are also permissible.
It has been recognized that basically material of the insert and/or of the housing is displaced during an interference fit. The groove provided according to the invention provides a defined location to which said material can preferably flow. After the installation is finished, the insert is firstly locked against the housing by the material located in the groove. Secondly, this material acts at the same time as a seal between the insert and the housing. A separate seal in the region of the interference fit is unnecessary.
The fitting of the insert into the housing can be implemented by forcibly pressing the insert into the receptacle or opening, by heating the housing and subsequently introducing the insert or by a combination of both measures.
The insert is advantageously a hollow cylinder with an open area and/or top surface. It is then suitable, for example, as a running face for a piston which is driven by a medium in the insert (cylinder liner) in an engine or conversely in a compressor which compresses the medium located in the cylinder liner. A hollow cylinder in principle has an outer wall.
The groove advantageously has a depth in the region of between 5% and 15% of the thickness of said outer wall. This is an optimum compromise between: (i) the stability of the fastening between the insert and the housing, said stability increasing as the depth of the groove increases; (ii) the quality of the seal between insert and housing, the quality tending to decrease above a certain depth; and (iii) the stability of the outer wall as such, the stability likewise having a tendency to decrease as the depth of the groove increases.
An outer wall of the insert and an inner wall of the housing advantageously surround a space in a liquid and/or gas-tight manner. A cooling medium, for example, can flow through such a space. Said space is substantially simpler to manufacture than a cooling space surrounded on all sides by the housing itself: if the housing is cast, a cooling space completely surrounded by the housing has to be kept free during casting by means of sand or similar means. It is difficult to fully remove said sand after the casting so that the sand does not enter the cooling circuit and, for example, damage a pump. Furthermore, the connections of such a cooling space through the wall of the housing to the outside and the closures thereof are susceptible to leakages. If, by contrast, a wall of the cooling space is formed by the insert, a corresponding clearance has to be drilled out as the sole additional manufacturing step at the housing.
This principle can be used not only in engines and compressors. A heat exchanger can also profit therefrom. In the case of a heat exchanger according to the invention, a liquid or gaseous medium can flow in each case both through the space between insert and housing and through the insert, and therefore heat can be exchanged between the two media through the wall of the insert. For example, a hot gas can flow through the insert, and a cooling medium can flow through the space between insert and housing. The improved seal according to the invention is substantially more stable in relation to changing temperatures than seals with O-rings according to the prior art.
The insert is advantageously manufactured from a harder material than the housing. The material of the housing is then preferably displaced when the insert is introduced into the housing. The material penetrates into the groove on the insert and engages behind said groove. Both the mechanical locking of the insert against the housing and the seal are then particularly good.
For example, the housing can be composed of aluminum, and the insert can be composed of cast iron, steel, a copper alloy or hyper-eutectoid aluminum. A crankcase, for example, can then be manufactured from lightweight aluminum without having to dispense with the advantages of the hard materials mentioned on the cylinder running face.
The groove advantageously has a width which is in the region of three to five times its depth. This is an optimum compromise between the stability of the mechanical locking between insert and housing, said stability having a tendency to become better as the width of the groove increases, and the quality of the seal, said quality having a tendency to become poorer above an optimum width.
For the same considerations, the groove preferably has a depth of between 0.4 mm and 1 mm, preferably between 0.4 mm and 0.8 mm.
In a particularly advantageous refinement of the invention, the housing is designed as a crankcase of an engine or compressor, and the insert is designed as a cylinder liner. This refinement solves the problems described at the beginning with the interference fit between cylinder liners and crankcases. According to the prior art, there is basically the problem that, in the case of an interference fit, the cylinder liner in some way channels a path into the housing material, with leakages arising because of the mutual deformation. The groove which is provided according to the invention provides a defined location to which the displaced material migrates. By this clearance being arranged on the insert, the material of the housing is preferably also displaced. The better mechanical locking leads to the cylinder liner no longer moving within the crankcase in operation. During the subsequent operation, the previously known misalignment of the cylinder center axis in relation to the axis of the crankshaft no longer occurs either. The two axes remain exactly in one plane. The clearance in the form of the groove leads to the displacement of material of the housing no longer, as previously, resulting in deformation of the cylinder bore.
By means of the improved mechanical locking between cylinder liner and housing, it is furthermore ensured that, after installation of the cylinder liner, the housing can still be mechanically machined to the full extent without destroying the alignment of the cylinder liner in relation to the cylinder bore in the housing. It is therefore no longer necessary to have completed all of the mechanical machining steps on the housing before the cylinder liner is finally fitted. In particular, during the mechanical machining, steps between the upper end of the cylinder liner and the upper top surface of the housing can be eliminated. The mechanical machining of the crankcase is required, for example, in order to form bearings for the crankshaft, flanges or the upper top surface of the housing. Furthermore, the cylinder liner itself can advantageously also be further processed after installation in the crankcase has taken place in order to optimize the cooperation of the cylinder liner with the piston during the subsequent operation. If a cooling space is not provided between housing and cylinder liner, the improved seal according to the invention continues still to be of advantage: it then protects the connection between cylinder liner and housing against undesired escape of oil.
Not all contact points between the insert (cylinder liner) have to be designed as interference fits. The interference fit provided according to the invention may also be combined with other types of fit.
The seal by the material penetrating into the groove can be improved further by introduction of a liquid seal.